The portable case that an artist uses for holding artwork is called a portfolio. These portfolios are often large and cumbersome. They’re flat, and have sides that can expand as more pieces are put into the portfolio. Some are flexible plastic, and these are often at the lower end of the spectrum. The higher end of the spectrum has metal cases that lock and can be rolled around instead of carried by hand. These higher end ones can sell for over one hundred dollars, while lower end portfolio cases sell for twenty to thirty dollars.
Portfolio folders are used to hold loose sheets of paper. This means papers that have come out of a worn out, older sketchbook or pieces that were done on printer paper or some other medium.